1. Field of the Invention
The present invention relates to a mobile radio system equipped with means for suppressing an output of interference radio waves in the technical field of mobile radio.
2. Description of the Related Art
FIG. 3 is a schematic diagram showing the structure of a conventional mobile radio transmitter. In FIG. 3, reference numeral 1 represents data to be transmitted, reference numeral 2 represents a transmitter unit, and reference numeral 3 represents an antenna. Data 1 is supplied to the transmitter unit 2, and is modulated and transmitted as a radio wave output 4 from the antenna 3. Reference numeral 5 represents a control CPU which supplies a transmission output control signal 6 to the transmitter unit 2. The transmission output control signal controls the on/off state of transmission, transmission power level, and the like.
A method of controlling the radio wave output of the mobile radio apparatus constructed as indicated above will now be described. Referring to FIG. 3, if there is data 1 to be transmitted, the control CPU 5 controls the transmission on/off state, transmission power level, and the like of a transmission power amplifier and the like in the transmitter unit 2. The data modulated at the transmitter unit 2 is transmitted as the radio wave output 4 from the antenna 1 at a predetermined transmission power level.
In the above-described manner, the control CPU controls the radio wave output of the conventional mobile radio apparatus described above.
With such a conventional mobile radio apparatus, however, if the control CPU controlling the transmission power of the mobile radio apparatus crashes or the hardware of the mobile radio apparatus breaks down, there is a possibility of transmitting radio waves at an unexpected timing or at an unexpected power level. For example, in a mobile radio system using CDMA (code division multiple access), users in one area are assigned the same carrier. Therefore, the radio wave output of one mobile radio apparatus may become interference to another mobile radio apparatus. It is therefore necessary for each mobile radio apparatus to control its transmission power correctly. If a mobile radio apparatus transmits its radio wave output at a power level larger than the predetermined level, another mobile radio apparatus may possibly be interfered with by the high-power radio wave output. In such a case, the number of users in one area must be reduced. The mobile radio system may become unable to operate if a mobile radio apparatus becomes defective and transmits too large a radio wave output.
The above-described problems are also associated with a parent-child communication system (JP-A-3-240328) in which any abnormality between a parent apparatus and a child apparatus is monitored.